This proposal describes experiments using the tools of mouse genetics to determine the in vivo functions of the c-abl proto-oncogene. The c-abl gene product is a cytoplasmic tyrosine kinase important for signal transduction and control of the cell cycle. Knock-out mice deficient in c-abl exhibit a number of phenotypes: perinatal lethality, runting, bone abnormalities, and defects in early lymphoid cell lineages. Several genetic studies of these mice are proposed. First, new alleles of c-abl will be generated by gene targeting ("knock-in" experiments). One of these alleles will permit the conditional deletion of the gene at selected times in development and in selected tissues; others will express altered forms of c-abl lacking particular domains responsible for protein localization. Examination of these mice should help determine the functions of each pathway emanating from c-abl; we will be particularly interested to examine the course of B cell development and the repertoire of variable region utilization. Secondly, a germ-line mutation of a new member of the Abi family termed PSTPIP1, a mammalian homologue of the yeast Cdc15 gene, will be generated by gene targeting, and the effects of the mutation alone and with other knock-out mutations will be characterized. Our expectation is that the loss of PSTPIP1 may suppress some of the phenotypes caused by loss of Abl. Thirdly, we will generate and analyze germ line mutations of the UV-DDB proteins, products of the xpe locus in man, and which we have shown are bound and regulated by the Abl kinase. Finally, we will directly catalogue the genes induced in cell lines and in tissues by oxidative stress, comparing the responses in abl mutants with wild-type controls, and thereby identify the Abl-dependent downstream targets. These studies should help define the many diverse functions of c-abl in mammalian development and physiology.